The present invention relates to a fluid-sealing nut and in particular to an improved method of making the same.
Sealing nuts of the present type are commonly used in the aircraft industry wherein many aircraft are designed with "wet" wings which require that the fasteners utilized in the wings form a fluid-tight seal. Currently, the most widely used type of sealing nut in the aircraft industry comprises a nut having an annular deformable sealing ring inserted into a counterbore cut into the bearing surface of the nut. Typically, the sealing ring is designed to protrude above the bearing surface of the nut so that when the nut is torqued down against the workpiece, the sealing ring is deformed inwardly into the threads on the shank of the bolt thereby forming a fluid-tight seal.
Sealing nuts of this type are generally made by a process whereby a counterbore is cold formed into the bearing surface of the nut and then an undercut is machined into the side walls of the counterbore to provide a means for retaining the sealing ring in place. The disadvantage of this process is that the undercut requires a separate machining operation which slows the production rate of the sealing nuts and hence significantly increases cost. Moreover, as with all cutting operations, the undercut surface creates a weakened stress point in the nut which restricts the torque and load limits of the nut.
The present invention seeks to eliminate these disadvantages by providing a new and improved method of making the above-described sealing nut. In particular, utilizing the method of the present invention, when the nut is initially cold formed according to conventional practice, a protruding ridge of excess material is purposefully retained around the periphery of the counterbore. When the nut is then cold formed a second time to smooth the bearing surface of the nut, the excess material is forced inwardly, thereby reducing slightly the surface diameter of the counterbore. In this manner, a means for retaining the sealing ring is created without requiring a separate machining operation and without weakening the structure of the nut. In fact, as will subsequently be explained in greater detail, the cold forming process of the present invention actually strengthens the load bearing surface of the nut. Thus, the resulting sealing nut produced is not only less costly to manufacture but is also a better quality nut.
Additional objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which make reference to the following set of drawings in which: